1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device preventing damage in an electrostatic discharge circuit and a manufacturing method thereof.
2. Discussion of the Related Art
The growth of the information technology and consumer electronics industries has driven the need for a next generation display device capable of processing and displaying the large capacity image information increases gradually.
Such next generation display devices are required to be lighter, thinner, shorter and smaller characteristics, a high luminance, a large-sized screen, low power consumption and a low price. Examples of next generation display devices include a liquid crystal display device (LCD), a plasma display panel (PDP), an electro luminescent display (ELD), and a vacuum fluorescent display (VFD). Among them, the LCD is the most widespread.
The LCD exhibits superior resolution compared to other flat displays, and a fast response rate comparable to that of the CRT in implementing a moving picture.
The LCD is widely used in various technology fields such as PC monitors, notebook computer monitors, TV receivers, vehicle-mounted TV receivers, navigation devices, and the like because it has high brightness and contrast and low power consumption.
Structurally, in the LCD, two substrates are arranged facing each other. Electrodes are respectively formed on facing surfaces of the two substrates. Liquid crystal is injected into a gap between the two substrates. An alignment state of the liquid crystal is changed by an electric field that is generated by a voltage applied to the electrodes. Accordingly, a light transmittance is varied and thus an image is displayed.
The LCD includes a liquid crystal panel for displaying an image and a driving unit for applying a driving signal to the liquid crystal panel. The liquid crystal panel includes first and second substrates attached together with a predetermined gap therebetween, and a liquid crystal layer injected into the gap between the first and second substrates.
The first substrate includes thereon a plurality of gate lines arranged in one direction to be spaced apart from each other by a predetermined distance, a plurality of data lines arranged perpendicular to the gate lines to be spaced apart from each other by a predetermined gap, a plurality of pixel electrodes formed in a matrix pattern in respective pixel regions defined by the gate lines and the data lines, and a plurality of thin film transistors (TFTs) that are switched by signals of the gate lines to transmit signals of the data lines to the respective pixel electrodes.
The second substrate includes thereon a black matrix layer for blocking light from regions other than the pixel regions, a color filter layer for representing color, and a common electrode for reproducing an image.
When the color filter is formed on an array substrate (that is, the first layer) including the TFTs, production yield and attachment margin can be improved.
A color filter on TFT (COT)-type LCD and a TFT on color filter (TOC)-type LCD in which a TFT and a color filter are formed on the same substrate will now be described.
FIG. 1 is a plan view illustrating a part of an array substrate for a related art COT-type LCD.
Referring to FIG. 1, a plurality of gate lines 152 are arranged in one direction on a substrate 150. A gate link line 154 is connected to one end of the gate line 152 and a gate pad 156 is connected to the gate link line 154. A plurality of data lines 158 are arranged perpendicular to the gate lines 152 to define a plurality of pixel regions P. A data link line (not shown) is connected to one end of the data line 158 and a data pad (now shown) is connected to the data link line.
An island-shaped gate pad port 153 is provided at the gate pad 156. The gate pad port 153 is connected to an external driving circuit to directly receive a driving signal therefrom.
A TFT T is formed at an intersection between the gate line 152 and the data line 158. The TFT T includes a gate electrode 160, an active layer 162, and source/drain electrodes 164 and 166.
A transparent pixel electrode 168 is formed in the pixel region P defined by the gate and data lines 152 and 158.
A black matrix 170 is formed on the TFT T, the gate line 152 and the data line 158. R/G/B color filters 171a, 172b and 172c are sequentially formed on the pixel electrodes 168.
In the above structure, the gate link line 154 and the gate pad 156 constitute a non-display region E and a TFT array region corresponds to a display region C. In the related art, light leakage occurs at a boundary region D between the non-display region E and the display region C.
FIG. 2 is an enlarged sectional view of a side taken along line I-I′ in FIG. 1. FIG. 2 illustrates an outer portion of the related art COT-type LCD.
Referring to FIG. 2, a COT-type LCD 190 includes first and second substrates 150 and 192 facing each other. The first and second substrates 150 and 192 are attached together using a sealant 194. A gate pad 152 and a gate pad port 153 connected thereto are exposed outside the sealant 194.
A polarization plate 196a is formed on an outside surface of the second substrate 192 and a polarization plate 196b is formed on an outside surface of the first substrate 150. Here, the polarization plate 196a has a polarization axis perpendicular to that of the polarization plate 196b. A top cover 198 is formed to cover around the peripheries of the first and second substrates 150 and 192.
The first substrate 150 includes thereon a TFT array region (not shown), color filters 172a, 172b and 172c formed on the TFT array region, and a black matrix 170 formed on the color filters. The second substrate 192 includes thereon a transparent electrode 199.
In the COT-type LCD 190, there occurs light leakage at the boundary region D between the non-display region E and the display region C, resulting in the degradation of an image quality.
To prevent this light leakage, the black matrix 170 must be formed also on the outer portion of the display panel as well as on the TFT region.
However, when the black matrix 170 is formed also on the second substrate 192 facing the first substrate 150, a second overcoat layer must also be formed on the black matrix 192 in order to reduce the step difference of the black matrix 170.
The second overcoat layer formed on the black matrix causes an undesirable increase in both the thickness of the LCD and its production cost.
Also, when an electrostatic discharge (ESD) circuit is formed at an end of an array portion in the first substrate, a contact hole must formed on the black matrix of the outer portion.
When the contact hole is formed on the black matrix, the material of the black matrix is transferred into the contact hole and thus an undesired organic layer is formed therein. Consequently, the manufacturing process becomes unstable and the quality or characteristic of the contact between the contact hole and the pixel electrode degrades.